Tube Preamp Reviews

Through the Ypsilon in passive mode, particularly the Schumann sounded moderately three-dimensional, with a wide stage perspective that was somewhat out of character for what, given the mid-hall balance. The same recording through the darTZeel NHB-108NS produced a fine but less transparent sound that was tonally cooler but equally spacious and precise. The strings were somewhat drier and the perspective slightly flatter, but the resolution of detail, particularly low-level information, was equally good. The stage width was identical, as were the dynamics. The biggest differences were in terms of harmonics and transparency: The Ypsilon produced more vivid colors, as well as a level of transparency and purity I'd never before experienced in my system.

I don't mean to exaggerate these differences—the sonic distance between the darTZeel and the Ypsilon wasn't enormous. Once my ears had settled in with either of these artifact-free sounds, I was always musically satisfied. But when I went back to the recording of Bruch's Scottish Fantasy, the Ypsilon reproduced Heifetz's silky tone and shimmering vibrato with greater physicality, and an intensity of texture and harmonic completeness that made his violin sound more lifelike.

In fact, there was no downside to the Ypsilon's sound with any genre of music. While in the UK recently, I picked up an original German pressing of Pat Metheny and Lyle Mays' intensely atmospheric As Falls Wichita, So Falls Wichita Falls (LP, ECM 1190). (A few weeks later I found myself in Wichita, on my way to Salina, Kansas, to visit Quality Record Pressing, Chad Kassem's new vinyl pressing plant—see this month's "Analog Corner.") Through the Ypsilon, the deep-bass strokes near the beginning of the title track, and the ensuing deep synth drones and richly recorded drum wallops, were reproduced with visceral intensity and their familiar full extension, while the shimmering bell trees produced fast transient shivers, and individual percussion notes rang with pristine clarity and no unnatural etch. Transformers can ring and produce a hazy aftertaste, in my experience, but the PST-100 Mk.II produced no such artifact.

And when "As Falls Wichita . . ." explodes about three-fourths of the way through its nearly 21 minutes, the Ypsilon did not restrain that macrodynamic thrust—there was nothing polite about this preamp's performance. But when called on to produce great delicacy, it did that as well. Active electronic stages often trade a modicum of transparency for a worthwhile increase in musical grip. In its passive mode, the PST-100 seemed to produce unprecedented transparency while exhibiting complete control and speed. Rhythm'n'pace were as honest and natural as the recording allowed.

Through the darTZeel NHB-18NS, the well-recorded Metheny-Mays LP sounded equally dynamic and wideband, but was slightly less transparent and spacious, less harmonically full-bodied, and sounded a bit grayed-out by comparison. Was that because the darTZeel doesn't pass along colors, or because the passive Ypsilon was adding them? I have no idea.

Going Active
Switching to active mode and raising the volume above the switchover point after the first six control steps to ascertain the sound of the Ypsilon's tube amplification section meant playing music loud, but I'm okay with that. (I used an SPL meter to match the levels, and never let the volume go above 95dB.)

Not surprisingly, the PST-100 in active mode sounded similar to the VPS-100 phono preamplifier. While the PST uses a different Siemens tube, the two components are more similar than different in design—and, of course, their transformers use similar technology, and are wound at the Ypsilon factory by the same team.

There was remarkably little difference between the PST-100's active and passive stages. I wouldn't want to be forced into a double-blind test here, but the active stage was just slightly darker, and more liquid or soft. Noise was nonexistent in passive mode, inaudible in active.

Going from the very fine solid-state darTZeel to the tubed Ypsilon and, months later, back again to the darTZeel, produced no surprises and only minor disappointment. Each is a world-class preamplifier: quiet, transparent, dynamic, and with a pure sound. Both handled the incoming signal precisely. They were more alike than different, but every difference favored the Ypsilon.

The Ypsilon's performance was equally good with rock, techno, jazz, and every other genre. XX, the Mercury Award–winning debut album by The XX (LP, XL LP450), aside from being very well recorded overall, contains some of the deepest notes I've ever heard from a record. The Ypsilon passed them along as well as the darTZeel does, with full extension and intensity. It also presented equally well everything else on XX, but with that bit of added transparency and clarity already noted.

If there was any downside to the Ypsilon PST-100 Mk.II in active mode, I didn't hear it—whatever faults JA's measurements might show were inaudible. Ypsilon specifies no signal/noise or harmonic-distortion specs for the PST-100 Mk.II, but based purely on what I heard, the preamp was essentially free of noise in passive mode, and equally quiet in active mode. In passive mode, if output-impedance variations reached the point where frequency rolloff occurred, I didn't hear it. In either mode, music erupted from jet-black backgrounds. If the measurements show any nonlinearities, they surely must be minor; the Ypsilon was as airy and extended and spacious on top, and as tight-fisted and extended on the bottom, as any preamplifier I've heard.

Conclusions
Ypsilon's PST-100 Mk.II is a full-function preamplifier that can drive most amplifiers in its passive mode, but can add a remarkably transparent, tube-based active stage when needed. It is beautifully and simply built using custom-designed transformers wound in-house, point-to-point wiring with custom-drawn silver wire, and hand-selected tubes designed for long, quiet, trouble-free use.

The PST-100 Mk.II is, as designer Demetris Backlavas modestly claims, "a fairly simple design." Simplicity can have definite benefits and equally definite costs—yet despite its minimalism, the PST-100 has no sonic or functional disadvantages that I could hear or experience. It seemed to add nothing to and subtract nothing from any signal it was fed. It didn't add noise or etch or edge, nor did it subtract transient clarity, dynamic slam, or frequency extremes. What it sounded like in active mode was the mythical straight wire with gain.

The preamp's six inputs should be enough for most audio enthusiasts, and its Tape Out is a useful addition for recording to any format. In the interests of sonic purity and circuit simplicity, the PST-100 Mk.II lacks a Mono switch or a Balance control—but if you're interested in maximizing transparency and accurate-to-the-source pass-through with attenuation and no resistors in the signal path, the Ypsilon PST-100 Mk.II is the best preamplifier I have ever heard.

At $37,000, the PST-100 Mk.II is very expensive; but given how it's made and how it sounds, and assuming you can afford it, it's well worth the money. For now, the Ypsilon PST-100 Mk.II is the most transparent and, therefore, the most perfect audio component I have ever heard—or not heard.